Water Comes Out Of Tap Perfect Ph But Very Low Alkanlinity

[Rob W]

I live in a small town on the Oregon coast and I believe our water supply comes primarily from rain water. Anyway, the water comes out of the tap at just about the perfect Ph of around 7.4. But the alkalinity is at between 20-30. Calcium is also very low at around 30. My spa manual says the ideal alkalinity for my spa is 125-150. The manual also says to adjust the alkalinity first, and then calcium (which is easy) and then Ph. But after raising the alkalinity to the 125-150 range, my Ph is sky high and I've had to add a bunch of Ph down. This time I was going to try and bring the Ph down first and then adjust alkalinity. But now I'm reading that if Ph is good not to worry about alkalinity? I'm confused.

[chem geek]

Don't raise the TA so high. Raise it only to around 80 ppm. The 125-150 ppm is a poor recommendation unless you find that your pH tends to fall over time, most likely due to continued use of Dichlor which is net acidic when accounting for chlorine usage. Basically, the TA is adjusted to get to a point of pH stability. If the pH tends to drop over time, raise the TA. If the pH tends to rise over time, lower the TA (but not below 50 ppm).

When you raised the TA to around 130 ppm from 25 ppm, the pH probably went from 7.4 to 8.0. If you only raise the TA to 80 ppm, it should go up to around 7.8 and you can add acid to lower the pH to 7.5 which will only slightly lower the TA level to 76 ppm. That's the easiest approach.

Higher TA, especially in a spa, leads to a rise in pH due to aeration which outgasses carbon dioxide from the water. Spas (and pools) are intentionally over-carbonated in order to provide a pH buffer and when plaster/grout is present, ti saturate the water with calcium carbonate to prevent dissolving such substances.

Richard

[Rob W]

Thank you very much! I will try that.

[Nitro]

Usually people have high Total Alkalinty (TA), and therefore need to lower it. I recommend lowering the TA to 80 ppm, and see how the pH acts. If the pH rises, I recommend lowering TA little more (60-70) etc.

HOWEVER, in your case I would only raise your TA to ~60 ppm, because you are coming up from the bottom. If you raise it to 80 ppm, you may find your pH rising too high.

I suggest raising your TA slowly until you get to the ideal range, rather than raise it to 80 only to lower it back to 60. You may find a TA at 60 is good. I would raise it to 60 to see how it acts. Then go from there.

Just my two cents, and I don't mean to disagree with Chem Geek. He's the expert around here.

[Vermonter]

Okay, kind of related, but since the topic seems to be basically closed, I don't feel as if I'm hijacking here.

I tend to find that my TA around 50 keeps my pH fairly stable throughout the week (I try to keep it around 7.5 to 7.8)... however, when I do go to readjust the following week, my TA has dropped to around 40, very occasionally even lower... how much of a concern should this be? When I enter the data into the "Pool Calculator" my calcite saturation index is still within the desired range (albeit close to the lower limit)... but then I bring it back up, wait a week, and repeat. My CH is 200, btw, in case that figures in somehow.

I'm really just responding to the fact that Richard said "but not below 50" in the post above, so I'm just checking here... thanks in advance for the input.

Tony

[chem geek]

Tony,

The TA is really there just for two reasons. One is to provide a pH buffer, especially against the pH getting too low from acidic sources. So if you don't have acidic sources (e.g. Dichlor, Trichlor, MPS, dry acid), then that's not a problem. At the other end, adding basic sources (hypochlorite chlorine such as bleach) will temporarily make the pH rise more when the TA is low so that can potentially lead to scaling if it went really high. For example, with a TA of 40 and CYA of 30, then adding enough bleach to raise the FC by 4 ppm would raise the pH from 7.5 to 7.94. Using 50 ppm Borates prevents this latter problem (the pH in my example would only rise to 7.6). So if you pH isn't swinging too wildly, then a low TA isn't a problem -- especially if you have Borates and use bleach, then I wouldn't worry.

As for the second reason, that's the saturation index so if it doesn't get too negative you're OK. Having a higher CH level lets you get away with a lower TA level, but just keep in mind that the CYA contributes about 1/3rd of its value to TA so with 30 ppm CYA and a TA of 40 this is really a carbonate alkalinity of 30. The Pool Calculator will figure this all out for you automatically if you put in the correct numbers. Also keep in mind that the TA test is +/- 10 ppm in accuracy.

My rule-of-thumb to never go below 50 ppm is mostly for safety reasons. If someone accidentally dumped some acid into the spa, then with too low a TA the pH could get very low and cause damage. Bottom line, it's your spa so if you find the pH isn't swinging too wildly and that the saturation index is close to zero or only somewhat negative (not below -0.3, for example) then you're fine. With your numbers, a TA of 50 is OK and 40 gets the saturation index to around -0.4 so I wouldn't stay in that situation long-term. It sounds like your pH swings so it's probably OK. If you had the water touching plaster/grout, then I'd be a little more concerned, but for general corrosion of metal and other parts, it's mostly pH that is an issue and not the saturation index. Remember that there are some people who run without added CH and some spas that use phosphate buffers that presumably don't get damaged -- the relationship between metal corrosion and saturation index is not a clear one. I think HHH mentioned pump seals as potentially being an issue, but except for dissolve of calcium carbonate in plaster/grout, it's low pH that is the primary factor in corrosion. Nitro's advice to be near a saturation index of 0 or slightly below is mostly just for safety to be sure.

Richard

[Vermonter]

Tony,

The TA is really there just for two reasons. One is to provide a pH buffer, especially against the pH getting too low from acidic sources. So if you don't have acidic sources (e.g. Dichlor, Trichlor, MPS, dry acid), then that's not a problem. At the other end, adding basic sources (hypochlorite chlorine such as bleach) will temporarily make the pH rise more when the TA is low so that can potentially lead to scaling if it went really high. For example, with a TA of 40 and CYA of 30, then adding enough bleach to raise the FC by 4 ppm would raise the pH from 7.5 to 7.94. Using 50 ppm Borates prevents this latter problem (the pH in my example would only rise to 7.6). So if you pH isn't swinging too wildly, then a low TA isn't a problem -- especially if you have Borates and use bleach, then I wouldn't worry.

As for the second reason, that's the saturation index so if it doesn't get too negative you're OK. Having a higher CH level lets you get away with a lower TA level, but just keep in mind that the CYA contributes about 1/3rd of its value to TA so with 30 ppm CYA and a TA of 40 this is really a carbonate alkalinity of 30. The Pool Calculator will figure this all out for you automatically if you put in the correct numbers. Also keep in mind that the TA test is +/- 10 ppm in accuracy.

My rule-of-thumb to never go below 50 ppm is mostly for safety reasons. If someone accidentally dumped some acid into the spa, then with too low a TA the pH could get very low and cause damage. Bottom line, it's your spa so if you find the pH isn't swinging too wildly and that the saturation index is close to zero or only somewhat negative (not below -0.3, for example) then you're fine. With your numbers, a TA of 50 is OK and 40 gets the saturation index to around -0.4 so I wouldn't stay in that situation long-term. It sounds like your pH swings so it's probably OK. If you had the water touching plaster/grout, then I'd be a little more concerned, but for general corrosion of metal and other parts, it's mostly pH that is an issue and not the saturation index. Remember that there are some people who run without added CH and some spas that use phosphate buffers that presumably don't get damaged -- the relationship between metal corrosion and saturation index is not a clear one. I think HHH mentioned pump seals as potentially being an issue, but except for dissolve of calcium carbonate in plaster/grout, it's low pH that is the primary factor in corrosion. Nitro's advice to be near a saturation index of 0 or slightly below is mostly just for safety to be sure.

Richard

Okay, this all makes sense to me, except for one little bit... I use Bromine, and occasionally (very occasionally) shock with bleach, but mostly with MPS, so I really have no idea what my CYA level is... I have this test available with my kit, should I run it just to find out? Or should it be essentially at zero? And if so, how does this affect where my numbers should be? This is something that has been bothering me for a bit now, so I'm glad I have a chance to bring it up... once again, thanks for the help!

T.

[chem geek]

Your CYA is probably zero since bromine tabs don't add it and it's not in tap water. That's fine and just means your carbonate alkalinity is the same as your TA. So when you're at 50 ppm, it's really 50 ppm. Again, the Pool Calculator will calculate things correctly -- just put in 0 for CYA. CYA doesn't do anything when you're using bromine so you don't need it. I'd just not overdo shocking with bleach (that is, don't add too much at one time) -- sounds like you mostly use MPS for re-activating the bromine anyway so that's fine.

Richard

[Vermonter]

Thank you again, Richard, for your support and advice.

Tony